Process for producing polybutadiene rubber and rubber composition

Abstract

A process for producing a vinyl-cis-polybutadiene rubber, including mixing (A) vinyl-cis-polybutadiene obtained by (1) a step of adding a cis-1,4-polymerization catalyst obtainable from an organoaluminum compound and a soluble cobalt compound to a mixture containing 1,3-butadiene and a hydrocarbon-based organic solvent as the major components and having an adjusted water content, thereby subjecting the 1,3-butadiene to cis-1,4-polymerization and subsequently, (2) a step of making a catalyst obtainable from a soluble cobalt compound, an organoaluminum compound represented by the general formula, AlR3 (wherein R represents an alkyl group having from 1 to 6 carbon atoms, a phenyl group, or a cycloalkyl group), and carbon disulfide present in the resulting polymerization reaction mixture, thereby subjecting the 1,3-butadiene to 1,2-polymerization; and (B) cis-polybutadiene obtained by a step of adding the foregoing cis-1,4-polymerization catalyst, thereby subjecting the 1,3-butadiene to cis-1,4-polymerization and a rubber composition containing the resulting rubber.

Description

TECHNICAL FIELD [0001] The present invention relates to a process for producing a vinyl-cis-polybutadiene rubber and in particular, to a process for producing a vinyl-cis-polybutadiene rubber having excellent extrusion processability, tensile stress and flex crack growth resistance, which is suitable for automobile tire members, especially sidewalls, and to a rubber composition using the subject rubber. [0002] Also, the invention relates to a rubber composition for sidewalls made of novel vinyl-cis-polybutadiene, which has a small die swell and excellent extrusion processability and which is capable of improving low fuel consumption with respect to a vulcanizate thereof. [0003] Also, the invention relates to a silica compounded rubber composition suitable for tire cap treads, which has a small die swell and excellent extrusion processability while keeping excellent wet skid performance, exothermic characteristic and abrasion resistance as required for the performance of tires such a...

AI Technical Summary

Benefits of technology

[0101] From the mixture containing unreacted 1,3-butadiene as remained after separating and obtaining the thus obtained VCR, the inert medium and carbon disulfide, 1,3-butadiene and the inert medium are separated by distillation. On the other hand, the carbon disulfide is separated and removed by an adsorption and separation treatment of carbon disulfide or a separation treatment of a carbon disulfide adduct, thereby recovering 1,3-butadiene and the inert medium which do not substantially contain carbon disulfide. Furthermore, 1,3-butadiene and the inert medium which do not substantially contain carbon disulfide can also be recovered by recovering the three components from the foregoing mixture by distillation and then separating and removing the carbon disulfide by the foregoing adsorption and separation or separation treatment of a carbon disulfide adduct. The thus recovered carbon disulfide and inert medium are mixed with 1,3-butaduene as newly replenished and then provided for use.

[0102] When continuous operation is carried out by the process according to the invention, it is possible to continuously produce VCR industrially advantageously with excellent operability of the catalyst component and in a high catalytic efficiency. In particular, it is possible to continuously produce VCR industrially advantageously in a high conversion without causing attachment to an inner wall in the polymerization tank, a stirring blade and other portions where stirring is slow. (B) Production of Cis-Polybutadiene

[0103] Cis-polybutadiene can be produced in the same manner as in the foregoing production process (A) which is used in the invention, namely the step of adding the cis-1,4-polymerization catalyst, thereby subjecting the 1,3-butadiene to cis-1,4-polymerization.

[0104] In general, the resulting cis-polybutadiene preferably has a content of the cis-1,4-structure of 90% or more, and especially preferably 95% or more.

[0105] The Mooney viscosity (ML1+4 at 100° C., hereinafter abbreviated as “ML”) is from 10 to 130, and especially preferably from 15 to 80. A gel matter is not substantially contained.

Problems solved by technology

When such a solvent is used, since the viscosity of a polymerization solution is high, there were problems in stirring, heat transfer, delivery, and so on, and excessive energy was required for recovering the solvent.

Furthermore, the foregoing vinyl-cis-polybutadiene rubber involved such a defect that it is inferior to usual high cis-polybutadiene with respect to exothermic characteristics and rebound resilience.

Furthermore, in general, it is known that a proportion of the tire rolling resistance occupying in the running resistance which largely affects the fuel consumption of an automobile is large and that the affect due to an energy loss of sidewall rubber is relatively large.

However, there is encountered such a problem that the die swell at the time of extrusion processing becomes large, and therefore, it is difficult to make the thickness of the sidewall member thin or to realize an enhancement of uniformity of tire.

In recent years, though there has been made a proposal to compound silica having excellent wet skid properties, thereby highly balancing the foregoing characteristics, such is not satisfactory yet.

However, such modification of the rubber tends to lower the wet skid properties.

The method for compounding a large amount of carbon black is not preferable because unification of rubbers is poor in the processing step, an electrical power load increases at the time of kneading or extrusion, and ML of the compounded material becomes large, whereby difficulty is accompanied at the time of extrusion molding.

The method for compounding a large amount of sulfur involves such defects that sulfur causes blooming and that the crack growth becomes fast due to an increase of the degree of crosslinking.

With respect to the addition of a thermosetting resin, since the thermosetting resin is low in compatibility with usually used natural rubbers or diene-based rubbers, when a large amount of the thermosetting resin is compounded, satisfactory dispersion is hardly obtained.

Furthermore, since this mixed compound is hard even in an unvulcanized state, the load may become large in kneading or extrusion, or the molding processability of tire may be deteriorated.

In a method for merely blending and compounding single fibers, since binding between short fibers and the rubber is insufficient, creep may become large, or fatigue life may be lowered.

However, these methods involve such problems that the elastic modulus or fatigue resistance of rubber is lowered and that the die swell becomes large.

However, since these short fibers are insufficient in adhesion to rubbers, there is encountered a problem that the fatigue life is short.

On the other hand, when a cap / base system is employed in passenger automobile tires, at the time of co-extrusion of a cap tread and a base tread, there is caused a problem that an extrudate is warped because of a difference in die swell between the both members.

If the die swell of the base tread rubber is made small, this problem is liable to be solved.

If a large amount of carbon black with high reinforcing properties is compounded, though the die swell become small, the heat generation becomes large.

In the case of using a steel cord, a very large strain is liable to be gathered in a rubber in the vicinity of the steel cord at the time of running of tire.

The method for compounding a large amount of carbon black is not preferable because unification of rubbers is poor in the processing step, an electrical power load increases at the time of kneading or extrusion, and ML of the compounded material becomes large, whereby difficulty is accompanied at the time of extrusion molding.

The method for compounding a large amount of sulfur involves such defects that sulfur causes blooming and that the crack growth becomes fast due to an increase of the degree of crosslinking.

With respect to the addition of a thermosetting resin, since the thermosetting resin is low in compatibility with natural rubbers or diene-based rubbers as usually used as a cord coating rubber, dispersion failure likely occurs, and crack resistance is deteriorated.

Furthermore, conventionally known tire cord coating rubber compositions are small in green strength.

However, in all of these methods, there may be the case where the heat generation at the time of repeated deformation becomes large, whereby the durability and fatigue resistance are lowered.